Project Summary/Abstract Declining mobility function is a common age-related phenomenon that is associated with reduced quality of life and high societal costs. Recently, the brain's critical role in mobility function has been recognized using imaging approaches assessing white matter characteristics. A new paradigm considering the brain as a complex network uses MRI to directly characterize the brain as a functional network. Brain Networks and Mobility Function: B-NET brings together national leaders in brain network science, neurology and mobility assessment to apply this innovative network paradigm to elucidate the aging brain's role in declining mobility. We propose that functional connectivity within and between the sensorimotor cortex -- community structure (SMC-CS) -- predicts declining mobility; and that SMC-CS will be associated with mobility independent of known relationships between white matter integrity and mobility function. B-Net will establish a cohort of 240 community-dwelling older adults (age range 70-85) and measure mobility function at baseline, 6, 18 and 30 months using the extended short physical performance battery (eSPPB). The MRI will be repeated at 30 months. B-Net's specific aims are to: Specific Aim 1. Determine the baseline association between SMC-CS and eSPPB score. We hypothesize that SMC-CS will be associated with eSPPB performance independent of known correlates of mobility function and white matter integrity (i.e. fractional anisotropy and white matter lesions). Specific Aim 2. Determine whether baseline SMC-CS predicts mobility decline. We hypothesize that poorer baseline SMC-CS will be predict declining eSPPB scores after accounting for known correlates of mobility impairment including white matter integrity, cardiovascular fitness, and muscle strength. Specific Aim 3. Repeat brain MRI imaging to determine the longitudinal association between changes in SMC-CS and changes in eSPPB score. We hypothesize that longitudinal declines in SMC-CS will be significantly associated with declining eSPPB performance independent of known correlates of lower extremity function decline and white matter integrity. B-NET tests a novel emerging paradigm regarding the CNS's role in age-related functional decline to support the development of innovative strategies to sustain mobility function in older adults, a critical public health need.